Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister coupled to the fuel tank which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon fuel vapor.
As the canister ages, the capacity of the adsorbent material to bind and release fuel vapor decreases. This may lead to an increase in emissions if the canister saturates with a reduced amount of fuel vapor. For example, during a refueling event, fuel vapor expected to be adsorbed into the canister may instead be vented to atmosphere. Some regions of the canister may see reduced purge air flow during purge events. Those regions may develop into a canister “heel” where the adsorbent is relatively saturated, and thus does not adsorb or desorb significant quantities of fuel vapor. This may lead to a scenario where the canister is saturated, and the purge event results in less fuel vapor being routed to the engine intake than expected.
In order to verify or diagnose the integrity of a fuel vapor canister, a canister working capacity diagnostic may be used to discern and quantify the ability of the fuel vapor canister to adsorb and desorb hydrocarbons. In this way, increased hydrocarbon emissions due to canister aging can be mitigated by servicing or replacing the fuel vapor canister. Other attempts have been made to determine fuel vapor canister working capacity. One example approach is shown by Glinsky et al. in U.S. Patent Application 2014/0324284. Therein, a dedicated temperature sensor is used to measure fuel vapor canister temperature, and the temperature readings used to determine a sorption capacity of the adsorbent. However, the inventors herein have recognized potential issues with such systems. Adding a separate canister temperature sensor increases manufacturing costs and canister complexity, and requires additional diagnostic routines to ensure that the temperature sensor is functional.
In one example, the issues described above may be addressed by a fuel system, comprising a solenoid valve positioned to regulate flow of fuel vapor between a fuel tank and a fuel vapor canister. The solenoid valve may include an indicator of changes in fuel vapor canister temperature resulting from fuel vapor adsorbing to adsorbent material within the fuel vapor canister. For example, the solenoid valve may be positioned such that changes in canister temperature are transmitted to a solenoid coil of the solenoid valve. The changes in temperature of the solenoid coil may be monitored at a controller, as the internal resistance of the solenoid coil varies based on temperature. In this way, the amount of fuel vapor adsorbing to or desorbing from the fuel vapor canister may be indicated without adding a dedicated temperature sensor to the fuel vapor canister.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.